Climate Science Glossary

Term Lookup

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Term:

Settings

Beginner Intermediate Advanced No DefinitionsDefinition Life:

All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 9 May 2015 by Guest Author

The US National Oceanic and Atmospheric Administration (NOAA) today announced that the monthly global average concentration of carbon dioxide surpassed 400 parts per million (ppm) in March 2015 for the first time since measurements began.

The average carbon dioxide concentration across the globe was 400.83 ppm,reportedNOAA.

If this news sounds familiar, it might be because this isn't the first time you've heard scientists mention the 400 ppm mark in recent years.

In the spring of 2012, NOAA reported all of its Arctic stations were measuring local concentrations of more than 400 ppm.

In 2013, the daily carbon dioxide concentrationsurpassed400 ppm mark attheMauna Loa Observatory, where scientists have been monitoring levels since the 1950s.

But March 2015 is the first time the average carbon dioxide concentration right across the globe has been more than 400 ppm for an entire month.

Global monthly carbon dioxide concentration. The dashed red line represents monthly mean values while the black line has had the seasonal cycle removed. Source: NOAA/ESRL

Plants and trees absorb carbon dioxide as they grow. This means concentrations of the gas rise and fall with the seasons, reaching a peak in May just before summer in the northern hemisphere. So, while carbon dioxide concentrations won't stay above 400 ppm for the whole year, we can expect them to remain high throughout May, said NOAA scientists today.

You can see the undulations of the seasonal cycle superimposed on top of the long-term rise in carbon dioxide over the past 35 years in this handy NOAA video.

Scientifically important or symbolic?

In terms of the global impacts of climate change, scientists don't attach much specific importance to the 400 ppm threshold. In other words, the consequences of climate change are not expected to change dramatically now that we've reached 400 ppm.

"It was only a matter of time that we would average 400 parts per million globally."

Professor Richard Allanfrom the University of Reading makes a similar point, telling Carbon brief recently that it's not surprising we find ourselves here. He says:

"[Approaching 400 ppm] is not significant in itself since a rise in global carbon dioxide concentrations above 400 ppm is inevitable".

While it carries no specific scientific meaning and has been on the cards for a while, passing 400 ppm is "a significant milestone", says Tans, because it hammers home how much human activity has contributed to atmospheric carbon dioxide levels - and how quickly. He says:

"This marks the fact that humans burning fossil fuels have caused global carbon dioxide concentrations to rise more than 120 parts per million since pre-industrial times … Half of that rise has occurred since 1980."

"This event is a milestone on a road to unprecedented climate change for the human race. The last time the Earth had this much carbon dioxide in the atmosphere was more than a million years ago, when modern humans hadn't even evolved yet."

In a year where hopes are high for governments to agree a deal to limit global emissions, surpassing the 400 ppm mark could well have more political significance than scientific. Hawkins adds:

"Reaching 400 ppm doesn't mean much in itself, but the steady increase in atmospheric greenhouse gases should serve as a stark reminder of the task facing politicians as they sit down in Paris later this year."

"That value in itself was not unanticipated but, worryingly, it has come even sooner than expected, indicating that the rate of increase is rising. The urgent need to address carbon dioxide emissions, in order to avoid dangerous future climate change, is very clear."

How do scientists measure carbon dioxide?

NOAA scientists collectairsamples from 40 stations all over the world and measure the number of molecules of carbon dioxide relative to the total number of molecules,after water vapor has been removed. This gives them what's known as the dry air fraction of carbon dioxide. Today's press release from NOAA explains:

"NOAA and partner scientists collect air samples in flasks while standing on cargo ship decks, on the shores of remote islands and at other locations around the world."

Dr Ed Dlugokencky, the NOAA scientist who manages the global network of monitoring stations, explains why it's important to get information from remote locations:

"We choose to sample at these sites because the atmosphere itself serves to average out gas concentrations that are being affected by human and natural forces. At these remote sites we get a better global average."

The best known of the world's carbon dioxide monitoring stations is the Mauna Loa observatory, which sits on the side of a Hawaiian volcano. Mauna Loa is home to the iconic Keeling curve - named after C. David Keeling who started the measurements in 1958. It is the longest standing continuous record of atmospheric carbon dioxide.

Comments

It appears that the rate of CO2 rise took a larger jump this year of 2.73 parts per million than in the last several years. In any case, recent claims that humans are putting less CO2 into the atmosphere appear untrue.

The victory of the Tory Party in the UK is a setback, since Labour had emphasized action against global warming in its campaign and the Tories have fought against land-based wind as unsightly and fought for fracking as well as reduced taxation of North Sea oil to improved the profitability of continuing extraction despite low prices.

At least China is cutting the amount of coal gasification they are planning. The future continues to look very grim. Hopefully, science will make batteries so good and electric transportation so much cheaper that gas and diesel vehicles will become comparatively expensive dinosaurs.

Re: TomR: It seems likely, though, that fossil fuel comanies will finance their own research to stay competitive and stay alive for a while yet. Should oil production not be stopped by market forces in time, the softest route left open would be for governments to make giving up the oil business as financially attractive as possible (rewards would be easier than punishments), while dismantling the oil-specific infrastructure wherever an oil firm calls it quits and banning new wells. This might be unpopular and dangerous, because it would involve transferring money to the rich, but it's preferable to no progress at all and to sabotage by frustrated citizens.

Part of the problem with just hoping fossil fuels will gow away is this; Every new coal fired plant or gas fired plant being built today is going to be around for decades. Govermnents and power utilities don't spend that kind of cash to shut them down after 5 years or so.

We need viable renewables sources now, and the sooner the better. I;'m not just talking about endless solar farms, etc. It's not working in Germany or China (never mind India). Those 3 countries (and others) continue to build coal and gas infrastructure.

@3, these are the problems that arise when governments pick winners aka intervening in the market place: the so called invisible hand of free-market theory can't operate efficiently... so when the phenomena of diminishing returns raises its ugly head how does a pastiche of next-to-random activity logically respond?

Economies are meant to be robust so let us all heil more government intervention to save our skin from the madness of Jevons Paradox!!

I'm glad this article specified that we are talking about 400 ppm as the monthly average. Too many media reports have just said 'first time ever'... which might cause confusion amongst those who remember readings hitting 400 ppm a couple years ago... as a daily total.

No doubt in another year or so we'll hit 400 ppm as the annual average.

As to the fossil fuel vs renewables and 'economics' debates. The victory of renewables is inevitable at this point. Today even the nominal price is cheaper than fossil fuels for more than 50% of the people on the planet, and if the difference in health, environmental, national security, and/or direct subsidy costs is factored in then fossil fuels aren't even close to competitive. All they've got going for them at this point is inertia... the existing infrastructure and vested interests will continue to prop up the facade of a fossil fuel future for a few more years. However, for anyone paying attention it is already clear that they are on the way out. It's really just a question of how many more years (decades are off the table) before they peak. I doubt we'll be able to stay under 2C, but 3C is now a real possibility.

Note the trend column in the monthly data, which just topped 399 in March. So, at current rate of over 2ppm/y, the trend will hit 400 in jsut 5-6months, very likely sooner than in a year.

As for your FF future assessment, unfortunately, there are big areas where FF cannot be replaced by renewables yet, e.g. transport, esp. aviation. That's why oil and gas still have future beyond your decadal limit. I agree with you with respect to coal: it's use as the source of energy should've already been superceded by cheper and cleaner renewables, political will being the biggest barrier at the moment.

@ 1 TomR, Both the Tory win and the battery hope are bad news. The good news is that if we look outside the box that we choose to think in, a solution is still possible for another 100 years or so. Political victory will go increasingly to the anti-climate control side, forever. One could extrapolate species self-extinction from this. People want more cars and junk, and they will do anything to get it. Self-delusion is no problem as we all know. As far as batteries? That’s a weak solution, the assumption is that renewable energy can then power our car cityscapes: 1) Pollution in creating the infrastructure, 2) expansion of demand to meet supply from car cityscape concept. 3) growing world wealth.

The good news is that at 20% of land, deserts represent about 100 million km2. Since they currently only hold less than 2 kg biological Carbon ( C ) per square meter. If these were forested C content could increase to 10 or even much higher, depending on water regimen. A little arithmetic tells us we could accommodate 160 GT into 20% of deserts. If we make them really rich forest, or sequester the biomass into the soil systematically, we can double that to 320 GT, then double the amount of desert we can take out 640 GT. That's greater than the current C budget for 2 degrees right?

The problem is our imagination is nailed down to old ideas, and new ideas must fit inside those old ideas. However, a good carbon-tax could free up our imagination through market mechanisms.

As far as batteries? That’s a weak solution, the assumption is that renewable energy can then power our car cityscapes: 1) Pollution in creating the infrastructure, 2) expansion of demand to meet supply from car cityscape concept. 3) growing world wealth

I think it is more than worth reminding ourselves what 'economics' means so, yes, considering exactly these types of points of view. There is an idea called Jevons Pardox which I think is what you talking about and more specifically how there must be a point of diminishing returns,... and a tipping point at that if I may!

PluviAL @8, according to wikipedia, the total land are of the Earh is 148.94 million km^2. The deserts of the Earth represent about a third of that, or 43.97 million km^2 if we sum the areas of the world's 10 largest deserts. That, however, includes 14.2 million km^2 from the Antarctic Desert, and 13.9 million km^2 from the Arctic desert. If nothing else, I think in any plan to tackle global warming we would want to keep both the Antarctic and Arctic deserts frozen (and have no choice in the short term for the Antarctic desert). That leaves approximately 20 million km^2 as the total available desert area for reforestation.

With a difference of C storage of 8 Kg per m^2, reforesting the 20 million km^2 would sequester at least 160 GtC, or the equivalent of 34 ppmv of atmospheric CO2 considering only the retained fraction in the atmosphere. That would indeed be a substantial contribution to combating global warming, but represents only 40% of the difference between current total cumulative emissions and the trillion tonnes of Carbon which is the upper limit to give us about a 2 in 3 chance of avoiding more than 2 C warming. Your C sequestration estimates are conservative, so it would not surprise me if you could double that, but not through reforesting more desert as there will not be more desert to reforest.

Having said that, reforesting deserts is a slow and complex process. You cannot plant trees in the Sahara and expect them to grow. You first need to build up a reasonable soil quality by planting arid friendly grasses. This would be a project over decades, and possibly centuries. We do not, however, have decades so the program, if pursued, would be a small supplement for mitigation by conversion to renewable technology, not a substitute for it.

Further, the energetics and engineering challenge of providing pipelines to water 20 million km^2 would be massive, not to mention the ongoing energy demands of desalinating and pumping the water. In addition, desert has a much higher clear sky albedo than does forest. Therefore your project could substantially increase the amount of solar energy absorbed. This is not entirely clear in that forests have much greater cloudiness than do deserts, but that in turn points to a substantial greenhouse effect from those clouds, and from the increased humidity in the formerly desert regions in general. It is beyond me to estimate the total forcing from such a project, but it may well be larger than that from the carbon sequestered. Finally, having grown up in a semi-desert, I have a fondness to arid landscapes. It is certainly not clear to me that we should condemn all the worlds desert species to exinction in our efforts to tackle global warming, as your plan would require.

An addendum to my @8, I should note that I am excited about new developments in battery technology. It is not that I think they are the way to a renewable future. It may turn out that Audi's e-diesel is the more economic option for transport, and systems similar to Isentropics pumped heat storage (both of which also excite me) are the better solution for standing power systems. What I want to see is multiple such developments competing in a world with a price on carbon. With such competition, the most economic overall system with the best side benefits will develop.

Tom Curtis @11, 100% in agreement with C-Tax to engage inventiveness of market.

@10, Thanks for excellent response, right as usual. My oops; top-of-hat calculation took the whole earth's surface instead of only land area. Forestation takes time, but plentiful water can reduce it by orders of magnitude. Living in the desert too, I have converted rocky lots into gardens in 2 years. Also, you are right 8kg/m2 is very conservative for sequestration.

Our reason for difference in appreciation of this line of attack is that I assume water can be pulled from the atmosphere at a negative cost. Process will produce electrical power as it is pulled out with nature's process. J. P. Espy's convection concepts is a starting ides. He was a founder of the science of meteorology. We know a lot more today than in the 1800. Burning forests is unnecessary, solar and latent heat energy are more than sufficient, and flow architecture can surpass natural precipitation production rates (conventional theory on this). As one byproduct, at 0.05% electrical production from free energy flux, a plant can produce more than a nuclear power plant, at <1/20th the cost, and mostly positive externalities. I'm working on a patent for that.

If it works, we can transport water in unlined canals specifically to percolate excess water from the oceans onto the earth, while absorbing CO2, and increasing forestation. I think the net radiation from earth increases with forestation, especially, if water for such growth is squeezed out of the subtropics as envisioned. The process concentrates heat in the upper atmosphere to radiate at k-temp difference to the 4th power.

Finally, I totally concur that desert habitat must be protected, but be we can afford to lose a lot more, hopefully redundant, desert than tropical forest at this time. Before proceeding with any of my ideas I expect many PHd's on each topic you point out to consider externalities.

A carbon tax, along with civic infrastructure improvement (laws which allow us to exclude, and move out troublesome people from communities, or with true rehabilitation which includes philosophical reprograming, nutritional re-regimentation, etc... etc... can allow for much more enjoyable walking cities and integrated communities. Such harmonious high density communities will be the biggest factor in reducing energy consumption as we confront the topic in full force at the end of the century. Markets can also be involved in this. Markets can also make this wild sounding idea practical and take the nasty sides out of it. ( I have a BA in sociology... but don't tell anyone from my U I am thinking these heretical thoughts.)

PluviAL @12, I am rather less sanguine than you about extracting water from the atmosphere in deserts, which are deserts (after all) because of the low relative humidity of the atmosphere over those latitudes. The only technique I know of that could reliably extract the moisture woud be to be to massively cooling the air, a process that will require a lot more energy than could be extracted by the condensation of water. Indeed, I suspect that extracting energy from water condensation would run up against entropy problems very quickly, and hence also not be feasible. However, if you invent a device that can do it, more power to you. On this I would be happy to be proven wrong, if only for the opening up of agricultural land on the fringes of deserts, and to regreen regions recently suffering desertification such as the Sahel.

chriskoz, aviation accounts for ~2% of emissions. Adding in the few categories of large ground vehicles which require an energy density that only fossil fuels can currently deliver might raise it to 3%. Thus, while I agree that we will likely continue to see some fossil fuel use for decades to come, I stand by my prediction that the peak of fossil fuel usage is less than a decade away.

Obviously, it will take time to replace the existing fossil fuel infrastructure with renewables, but we are very near (possibly even past) the turning point. Total CO2 emissions basically held steady last year despite global GDP growth. Trends so far this year suggest that CO2 emissions may well drop.

We talk about environmental tipping points, but such things also exist in politics and economics. We are very close to the point where renewables finish supplanting fossil fuels as the darlings of the global economic and political castes. Soon they will be growing not just because they are better, but also because they will be propelled by the same forces which have thus far been deployed to hold them back.